Question

Sam drove $96$ miles in $90$ minutes. His average speed during the first $30$ minutes was $60$ mph (miles per hour), and his average speed during the second $30$ minutes was $65$ mph. What was his average speed, in mph, during the last $30$ minutes?

$64$

$65$

$66$

$67$

$68$

Answer: D

Concepts:distance rate and time

Difficulty rating: 980

Solution:

Each leg is half an hour. In the first, Sam drove $60 \cdot \tfrac12 = 30$ miles; in the second, $65 \cdot \tfrac12 = 32.5$ miles. That's $62.5$ miles so far. That leaves $96 - 62.5 = 33.5$ miles for the last half hour, which is a speed of $33.5 / \tfrac12 = 67$ mph. Therefore, the answer is D.

2018 AMC 10B Problem 2

Answer: D

Difficulty rating: 980

Solution:

Problem 2 in Other Years